Led by Michael R. Vanner in Prof. Markus Aspelmeyers Aspelmeyer Group for Quantum Foundation and Quantum Information at the Nano- and Microscale, the team  which also included I. Pikovski, G. D. Cole, M. S. Kim, Č. Brukner, K. Hammerer, and G. J. Milburn  faced a number of challenges in devising their optomechanical scheme to fully reconstruct quantum states of mechanical motion. One of the most fundamental is the attempt to observe quantum mechanical behavior of a macroscopic mechanical object, since any potential quantum features would exhibit themselves only on truly miniscule scales. For the mechanical structures that we consider, Vanner explains, one needs to resolve position displacements of about a femtometer, or one-trillionth of a millimeter. This is a mind‐bogglingly small distance that is, in fact, smaller than even the diameter of a hydrogen nucleus.

This then leads to additional challenges: In the attempt to measure an objects position, the object moves and causes positional smearing by injecting uncertainty into the resulting position information, which is referred to as the Standard Quantum Limit (SQL). The first challenge that we had to overcome was to find a method which circumvents the SQL, Vanner continues. The second was that making measurements of the position alone is insufficient to reconstruct a quantum state. This is because the quantum state contains all that is, at least in principle, knowable about the object. And so, one needs to also measure all the complementary properties of the state, such as its momentum, and to do so also in an equally precise manner.

Since no existing microscopy technology is capable of resolving quantum-scale features, the team addressed these challenges with optical interferometry. Perhaps where we benefited most, Vanner reflects, was from the work of V. B. Braginsky, who made several seminal contributions to the field of quantum measurement1. In particular he introduced a scheme using short pulses of light that can overcome the SQL. A short pulsed interaction can achieve this because the mechanical object has very little time to move during the interaction, and thus smearing can be dramatically reduced. Braginsky developed this technique to make sensitive force detectors with the goal of detecting gravitational waves, notes Vanner. Weve utilized this technique to allow for very sensitive position measurements. What we introduce in our proposal is a protocol using these pulsed measurements to perform quantum state reconstruction, which was our primary interest, and also a protocol to prepare low entropy squeezed states.

The state reconstruction scheme works in much the same way as many modern medical imaging techniques  that is, by taking images from many angles, as in X‐ray computed tomography, it is possible to determine the three-dimensional internal structure within the body. Applying this analogy to our case, Vanner continues, the internal structure is the quantum state and the angles are its various properties: position, momentum, and their combinations. Our state reconstruction protocol uses appropriately timed pulses of light to access all these properties, thus providing a means to determine all the information in the quantum state. An important point is that the team has analyzed the experimental feasibility and demonstrated that the scheme is realizable with current state‐of‐the‐art technology.

Vanner is optimistic about the development of additional innovations and extensions in pulse sequences and measurements based on their pulsed design. As an example, Vanner notes, were currently trying to compliment our work reported in PNAS by developing pulsed approaches to quantum state preparation. Combining such results with our state reconstruction results provides a complete experimental framework.

In terms of how their findings might enhance the future exploration of quantum mechanical phenomena on a macroscopic scale, Vanner points out that one important quantum mechanical phenomenon that is little explored in the laboratory is decoherence  the term given to the processes by which the environment surrounding a quantum object gains information about its state, often leading to the undesirable consequence of loss of quantum coherence between superposition components. Decoherence is often regarded as one of the primary hindrances in efforts to construct a quantum computer. The quantum state tomography scheme that we have introduced can be used to observe and characterize decoherence, thus providing vital experimental data for the development of quantum mechanics based technology.

Moreover, adds Vanner, It is a fascinating prospect that quantum information can be encoded into the motion of a mechanical object. This may lead to a number of interesting possibilities, such as transduction between flying qubits  i.e., photons  and qubits in a solid state device or superconductor. A pulsed approach may indeed be a feasible route to achieving this goal.

In addition to decoherence as discussed above, adds Vanner, An attractive feature of the quantum state reconstruction scheme is that it can reconstruct and analyze any quantum state of motion. Thus, a large number of state‐dependent quantum effects can be studied. For example, one could utilize the fragility of a quantum superposition state as an extremely sensitive detector.

For Vanner, one of the key prospects is to see their design actually realized. Were currently building an experiment to implement our quantum state reconstruction protocol, he concludes. Im finding it very exciting to be able to physically implement our ideas and begin to experimentally see behavior that is predicted in our theoretical model.

Related Stories

Just as a camera flash illuminates unseen objects hidden in darkness, a sequence of laser pulses can be used to study the elusive quantum behavior of a large "macroscopic" object. This method provides a novel tool of unprecedented ...

(PhysOrg.com) -- "Many people are trying to build a quantum computer," Olivier Pfister tells PhysOrg.com. "One to the problems, though, is that you need hundreds of thousands of qubits. So far, scalability has been something ...

Researchers at the University of Calgary, in Canada, collaborating with the University of Paderborn, in Germany, are working on a way to make quantum networks a reality and have published their findings in the journal Nature. ...

(PhysOrg.com) -- Few people doubt the "quantumness" of entanglement. Quantifying the quantum correlation of entanglement is something that is relatively regular right now. However, things change a bit when it comes to quantum ...

(PhysOrg.com) -- The ability to entangle particles is considered essential for a number of experiments and applications. While we have seen evidence for quantum entanglement, it is still difficult to detect unambiguously. ...

Recommended for you

In microelectronic devices, the bandgap is a major factor determining the electrical conductivity of the underlying materials. Substances with large bandgaps are generally insulators that do not conduct electricity well, ...

Since the early 20th century, nearly all of Earth's glaciers have been retreating or melting. Glaciers cover 10 percent of the planet's land area and contain 75 percent of our fresh water. Moreover, the water from melting ...

Researchers in Eindhoven have developed a new type of low-energy, nanoscale laser that shines in all directions. The key to its omnidirectional light emission is the introduction of something that is usually highly undesirable ...

A pair of researchers, one with the Public University of Navarre, the other with the University of Bristol, has developed a system of holographic acoustic tweezers that can be used to manipulate multiple objects simultaneously ...

In order to evaluate a material's ability to withstand the high-radiation environment inside a nuclear reactor, researchers have traditionally used a method known as "cook and look," meaning the material is exposed to high ...

everything is already entangled and it is the isolation from entanglement with everything else that is the state we observe and label as entanglement. That is why there is a distance limit on entanglement, because interferance from everything in between makes isolation of the entangled pair impossible (or at least improbable).

"Einstein infamously dismissed quantum entanglement as spooky action at a distance and quantum uncertainty with his quip that God does not play dice with the universe. Aside from revealing his conceptual prejudices, Einsteins rejection of these now-established hallmarks of quantum mechanics point to the fields elusive nature:"

Good grief Phys Org! He didn't dismiss entanglement, he was describing it. And he felt that uncertainty was a manifestation of a deeper classical principle. He didn't dismiss it either, he just didn't like it.The man played a foundation role in developing Quantum Theory and yet you display a complete ignorance of that role and his opinions.

Einstein's brilliance was such that he could see where quantum mechanics was flawed or at least seemed to be self contradictory. The real issue with "spooky action at a distance", is the issue over the measurement problem. Because quantum mechanics has to account for all possible states in a system to produce any testable statements, you will often find that it predicts things such as entanglement, which while verifiable per se, have no real meaning in a practical sense. Entanglement is one of the by-products of considering the system as a whole, or taking the "Holistic approach" to theory. In practice we find that while this is reasonable and often shows experimental results that imply that this does truly approach the nature of quantum reality, at the more classical or macroscopic level it is irrelevant. We simply cannot and do not experience this reality on a macroscopic scale.Good Idea to test it to see if we can though.

Entalgement in strict sense may not be percievable on a macroscopic scale, but it seems that non-locality in general can be seen at all levels of complexity. For example social and other systems, alleged telepathy and other psi phenomena (if you consider them "real")... But I'm not a physicist, just thinking.

Please sign in to add a comment.
Registration is free, and takes less than a minute.
Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.